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1TB Fusion / 24GB SSD
- Thread starter marty1990
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You do realize in order for the Fusion drive to 'Hide' the sluggishness of the HDD, it will always try to cache up to 4gb of writes at a time in which it will later write that data onto the HDD during idle. So if a user were writing 50gb of data per day - not all at once, but in smaller files in increments - (which is actually quite unlikely) you would be putting 50gb of wear on the puny 24gb SSD. Again, for the average Instagram/Facebook/iTunes iMac user, they're not going to be getting that much more out of their machine by upgrading to a full SSD. This 24gb SSD/1TB HDD should've been the base option at least considering how cheap flash ram is nowadays.
This is a total misunderstanding of how Fusion works.
Fusion only loads BLOCKS to the SSD - not the entire OS, not entire apps, not entire files, just that code/data that is required. The only parts of the OS that will be on the SSD will be the parts you use (although, at under 8 GB, even the entire OS would not overwhelm a 24GB SSD). The only parts of your apps that will be loaded, ditto, data, ditto. OS X manages the SSD the way that it manages RAM - it knows what you need, it knows what you use, it knows what hasn't been used lately, and it puts it/leaves it/removes it from fast storage as required.
(Now, the people who insist on splitting their Fusion systems so that they can put their entire OS and all their apps onto Flash are doing as you describe - a totally wasteful, overly-simplistic practice, if you ask me.)
One can look at going from 128GB to 24GB to be a downgrade, but I'd look at it as more of an upgrade. Reducing the amount of Flash storage reduces the selling price, making Fusion more affordable as an entry-level feature. Will the performance of a 24GB Fusion system be the same as the 128GB? I can't see how. However, Apple has had several years of field data more than it had when the feature was introduced - whatever the performance hit may be, I suspect for light/moderate use, there will be little or no perceivable difference in performance.
The message to me is pretty simple; the people who need more RAM are likely to need more Flash, and will buy more of both (whether as Fusion or pure Flash). Other people will buy more RAM and Flash than they really need. Others will find that Apple's base configuration works great for their needs.
That's not how fusion drive works.
It's not an hybrid hard drive. The SSD section isn't a cache, so it's not caching every data file the user access.
More often used files are stored in the SSD for quicker access. There are much more reads than writes on the SSD for a fusion drive.
Read this page below and educate yourself
http://www.anandtech.com/show/6406/understanding-apples-fusion-drive
They're not the only ones to see this behavior too, many other sites have also observed this behavior.
As it is dividing files for faster access, does the Fusion Drive system copy files to the SSD, or are they moved?
I ask this thinking about SSD failure. If the SSD fails, are all the files (OS, saved documents, etc.) available on the still working spinning hard drive for recovery?
I ask this thinking about SSD failure. If the SSD fails, are all the files (OS, saved documents, etc.) available on the still working spinning hard drive for recovery?
actually you seem to be the one to be educated:
Originally I thought this might be SSD caching but after poking around the new iMacs and talking to Apple I have a better understanding of what's going on.
...
That 4GB write buffer is the only cache-like component to Apple's Fusion Drive. Everything else works as an OS directed pinning algorithm instead of an SSD cache. In other words, Mountain Lion will physically move frequently used files, data and entire applications to the 128GB of NAND Flash storage and move less frequently used items to the hard disk
Fusion Drive doesn't use SSD as a cache.
it's not entirely clear, but I think they are MOVED, not copied.
So if the SSD fails, the system is corrupted.
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Wouldn't data corruption be a possible problem as well if files are moved back and forth across drives, rather than copied? The drives could be operating as they should, but then files are written incorrectly by the OS and...the whole thing collapses! Seems very basic to me. Apple must have considered this very real and likely possibility.
I assumed that since the SSD is never included in the total Fusion Drive storage total, files were copied.
I assumed that since the SSD is never included in the total Fusion Drive storage total, files were copied.
PLEASE READ THE ARTICLE: Doesn't this below describe what a cache is?!!!
With Fusion Drive enabled, Apple creates a 4GB write buffer on the NAND itself. Any writes that come in to the array hit this 4GB buffer first, which acts as sort of a write cache. Any additional writes cause the buffer to spill over to the hard disk. The idea here is that hopefully 4GB will be enough to accommodate any small file random writes which could otherwise significantly bog down performance. Having those writes buffer in NAND helps deliver SSD-like performance for light use workloads.
Since any data written to the fusion drive that's smaller than 4gb will always be written to the SSD first. That's a drive cache, therefore if you wrote 17 3gb files during the day, you've essentially written and erased over 50gb of data on the SSD. That's a lot more wear on a 24gb SSD than a 128gb that's over 5x larger. And the wear is even worse as most of the other 20gb will be taken up by program files that OS X wants to keep in the SSD to speed things up. This allows less wear leveling.
this seems quite clear to me:
That 4GB write buffer is the only cache-like component to Apple's Fusion Drive. Everything else works as an OS directed pinning algorithm instead of an SSD cache. In other words, Mountain Lion will physically move frequently used files, data and entire applications to the 128GB of NAND Flash storage and move less frequently used items to the hard disk.
frequently used files are stored, and stay, on the SSD storage.
You have to continuously change used files to wear the SSD, which is highly unlikely.
I guess I need to draw this out for you
1. Traditional HDD
CPU----DATA----DATA written directly to HDD
2. Fusion
CPU----DATA----ALL DATA Written to SSD FIRST up to 4gb total file size----Idle---Transfer SSD data to HDD, Rinse-repeat.
So you write 50gb of data throughout the day, you will write/erase 50gb of data off/on the SSD as it will all pass through the fusion drive unless it's larger than 4gb.
In an effort to give the impression to the end user that the Fusion drive is fast, the data will always be written first to the SSD. If the user had to wait for the files to be written to HDD first, it would feel as slow as a regular HDD during writes and only feel as fast as a SSD during reads (if the data is already in the Fusion SSD). Blackmagic isn't lying when it says 600+mb/sec writes on a fusion drive (which no single HDD is capable of those speeds with today's technology) It's showing that the data is being first written to the SSD before it's written to the HDD. That is a cache, it's a 'smart cache' as OS X will keep frequently used files like OS files on the SSD, so it's better than a plain ol dumb regular cache.
Here's another article written by OWC
http://blog.macsales.com/19994-further-fusion-testing
And I quote "The other half of the performance benefit is that Fusion Drives maintain a 4GB buffer space on the SSD. This means files written to the Fusion Drive are written to the SSD first and then migrated to the HDD when the drive is idle."
1. Traditional HDD
CPU----DATA----DATA written directly to HDD
2. Fusion
CPU----DATA----ALL DATA Written to SSD FIRST up to 4gb total file size----Idle---Transfer SSD data to HDD, Rinse-repeat.
So you write 50gb of data throughout the day, you will write/erase 50gb of data off/on the SSD as it will all pass through the fusion drive unless it's larger than 4gb.
In an effort to give the impression to the end user that the Fusion drive is fast, the data will always be written first to the SSD. If the user had to wait for the files to be written to HDD first, it would feel as slow as a regular HDD during writes and only feel as fast as a SSD during reads (if the data is already in the Fusion SSD). Blackmagic isn't lying when it says 600+mb/sec writes on a fusion drive (which no single HDD is capable of those speeds with today's technology) It's showing that the data is being first written to the SSD before it's written to the HDD. That is a cache, it's a 'smart cache' as OS X will keep frequently used files like OS files on the SSD, so it's better than a plain ol dumb regular cache.
Here's another article written by OWC
http://blog.macsales.com/19994-further-fusion-testing
And I quote "The other half of the performance benefit is that Fusion Drives maintain a 4GB buffer space on the SSD. This means files written to the Fusion Drive are written to the SSD first and then migrated to the HDD when the drive is idle."
All in all I'd hope everyone got Apple Care, @ 2K$ I'd hope you would, if you a problem 2 or 3 years down the road take it to Apple and get it fixed/replaced. My Apple store and AAL said if anything happened, say like the SSD portion of the fusion died I could get it replaced or pay the difference for or price for any SSD replacement and then that would have a warranty as well.
I think this is all good information regarding the 24gb SSD, but IMO I don't think it's likely that Apple put it in there knowing or thinking it would die in 2 or 3 years, not to say that they wouldn't because I don't know. But that has not been my experience with Apple products. I think if you're really that worried about it, just go SSD all out and use external for other needs. Personally when and if mines bites, I'll open it up if the warranty is done and replace it myself. I've also take with others who build computers regularly as well and the general census is to not be concerned with the cycles but rather the amount. And as usual most companies post soft results to "CYA" but hardware usually last longer than stated. That's all just my opinion and experience based on some research, some conversation and anecdotal evidence.
If you're really that concerned, the way I see it is, it's a few now or a few hundred later with a headache.
I think this is all good information regarding the 24gb SSD, but IMO I don't think it's likely that Apple put it in there knowing or thinking it would die in 2 or 3 years, not to say that they wouldn't because I don't know. But that has not been my experience with Apple products. I think if you're really that worried about it, just go SSD all out and use external for other needs. Personally when and if mines bites, I'll open it up if the warranty is done and replace it myself. I've also take with others who build computers regularly as well and the general census is to not be concerned with the cycles but rather the amount. And as usual most companies post soft results to "CYA" but hardware usually last longer than stated. That's all just my opinion and experience based on some research, some conversation and anecdotal evidence.
If you're really that concerned, the way I see it is, it's a few now or a few hundred later with a headache.
You do realise Apple have changed the algorithm that determines what gets written to the SSD? I wouldn't trust these articles from 2 or 3 years ago.
The need for a large SSD component is overblown imo. I don't think you would even need a 128GB SSD unless you are frequently working with many large applications, or many large media files (and NOT storing those media files on external RAID/Thunderbolt drives).
That is an unusual use-case scenario because most media professionals would be running externals drives for their data.
The Black Magic Test is writing 5GB by standard configuration and I got the same speed before and after disabling the 2TB Fusion Drive in my new iMac.
The 128GB SSD is much slower in writing than the larger ones, it should be nearly the same as reading. I'd be interested in the speed of the 24GB SSD.
Sadly I did not backup the screenshot before splitting the drives and now I don't have the iMac anymore.
128GB SSD vs. 2TB HDD (7200rpm):
The 128GB SSD is much slower in writing than the larger ones, it should be nearly the same as reading. I'd be interested in the speed of the 24GB SSD.
Sadly I did not backup the screenshot before splitting the drives and now I don't have the iMac anymore.
128GB SSD vs. 2TB HDD (7200rpm):
According to your logic hybrid HDD (with an SSD cache usually of 8 Gb) expected lifespan is within 6 months....
Pretty credible.
I'd say so. 100GB of extra flash buffer for the fusion drive, 1TB of extra HDD storage, a faster CPU and a faster GPU would be worth the $300 premium to me.
The only upgrade i'm mixed on is the M395X upgrade at $250. That upgrade should be $150 at the most.
1. Hybrid drives like Seagate's Momentus XT Don't cache writes - so your argument is moot
2. Seagate Momentus XT drives use SLC Flash ram which is designed to withstand >100,000 P/E cycles. Much more durable than latest gen TLC/MLC cheaper flash found on Apple's SSD's which is only rated for 1,000-3,000 P/E cycles
Apple's chosen to ignore the capacity of the SSD when marketing Fusion, but rounding of that sort regarding storage capacity has always gone on, throughout the industry. Does a 1 TB HDD really offer 1,000,000,000,000 bytes of usable storage? No, exactly how much it can store will depend on the OS and formatting.
Data corruption is always a possibility, on any system - every time a byte is written or read. It doesn't really matter whether the copy/move is from one HDD to another, or between SSD and HDD, from HDD or SSD to RAM, from RAM to CPU... the system has methods for validating all of this. None of this operates without a safety net.
Our layman's understanding of terms like Move and Copy do not jibe with the way the processes work. For example, a Move within a physical HDD changes the directory listing for a file, but the data remains in the same physical location on disk.
Jeez this is really confusing! I want to buy the 4K iMac (I don't want the 27 as it's too big). I am a casual user, I don't do any video editing or use any other heavy software. I'll use it for email, web browsing, watching films and using MS Office. I do play The Sims though and other games of that ilk, city builders etc. Would the 2TB fusion suffice for my needs; I would hope so but it's very confusing!
In hybrid drive NAND is primarily used to service read operations. Writes to the flash memory by the device controller occur following a read/write modification, or when more relevant data is transferred to NAND to help accelerate subsequent read operations. When a file (or a portion of a file) held in NAND is subject to a read/write modification, the revised data is modified on the hard disk platter first before it's copied back to the NAND. As a consequence, data integrity is reliant on the mechanical storage, rather than whatever is sitting in the solid-state space.
All your statements about expected P/E cycles on hybrid drive and Apple SSD are baseless....
The 2tb fusion is more than good enough. In fact it was made for your uses.
Any one out there with the new 1TB fusion?
I'm interested in the black magic test results as well.
If i order the new iMac 5k with 1TB Flash Drive and the following specs. i7, 16GB RAM, AMD 4GB will I be ok with performance or doesn't make it sense to order it with this specifications?